Substituted amphetamines such as methamphetamine (METH) and 3,4-methylenedioxymethamphetamine (MDMA; 'ecstasy') are synthetic drugs which are widely abused as psychostimulants. In recent years, there is a growing epidemic of METH and MDMA abuse not only in urban areas, but also in many rural parts of the US that were previously unexposed to psychostimulant abuse. Repeated use of METH and MDMA causes the development of severe addiction, aggression, violent and psychotic behavior, memory loss, and potential dopaminergic and serotonergic neurotoxicity. Currently, there are no pharmacotherapies against substituted amphetamines addiction and neurotoxicity. The long term goal of this project is to identify potential pharmacotherapies against amphetamines addiction. Our recent studies suggest that besides the role of dopamine in the action of psychostimulants, nitric oxide (NO) may play a pivotal role in mediating the effects of these drugs. In brain, NO is produced by the neuronal, inducible and endothelial nitric oxide synthase isoforms (nNOS, iNOS, eNOS) and has been implicated in neural transmission, plasticity and neurotoxicity. We hypothesize that nNOS has a major role in 1) the psychomotor stimulating effects, 2) the reinforcing properties and 3) the dopaminergic neurotoxicity produced by substituted amphetamines. Accordingly, the specific goals of this proposal are: 1) To investigate the effects of selective NOS inhibitors on the development of behavioral sensitization to substituted amphetamines, and the effects of the latter on nNOS and iNOS knockout (KO) mice. Potential alteration in the expression of the NOS protein levels in correlation with behavioral sensitization will be investigated. 2) To examine the role of NOS isoforms in the rewarding effects of amphetamines. The effect of NOS inhibitors on amphetamines-induced conditioned place preference (CPP) will be investigated, and the effects of the amphetamines on the acquisition of reward in NOS KO mice will be determined. 3) To investigate the role of nNOS and iNOS in dopaminergic and serotonergic neurotoxicity elicited by various amphetamine analogs, and whether alteration in the expression of NOS proteins is associated with neurotoxicity. The proposed studies will utilize pharmacologic, genetic, and molecular techniques to investigate the role of NO in amphetamine-induced behavioral sensitization, reward, and neurotoxicity. The combined behavioral, neurochemical and molecular approaches designed will lead to better understanding of the mechanisms underlying the effects of substituted amphetamines and the development of new therapeutics for the management of amphetamine addiction and toxicity.